<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
  <head>
    <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
    <title>Auto Commit</title>
    <link rel="stylesheet" href="gettingStarted.css" type="text/css" />
    <meta name="generator" content="DocBook XSL Stylesheets V1.73.2" />
    <link rel="start" href="index.html" title="Getting Started with Berkeley DB Transaction Processing" />
    <link rel="up" href="usingtxns.html" title="Chapter 3. Transaction Basics" />
    <link rel="prev" href="abortresults.html" title="Aborting a Transaction" />
    <link rel="next" href="nestedtxn.html" title="Nested Transactions" />
  </head>
  <body>
    <div xmlns="" class="navheader">
      <div class="libver">
        <p>Library Version 11.2.5.3</p>
      </div>
      <table width="100%" summary="Navigation header">
        <tr>
          <th colspan="3" align="center">Auto Commit</th>
        </tr>
        <tr>
          <td width="20%" align="left"><a accesskey="p" href="abortresults.html">Prev</a> </td>
          <th width="60%" align="center">Chapter 3. Transaction Basics</th>
          <td width="20%" align="right"> <a accesskey="n" href="nestedtxn.html">Next</a></td>
        </tr>
      </table>
      <hr />
    </div>
    <div class="sect1" lang="en" xml:lang="en">
      <div class="titlepage">
        <div>
          <div>
            <h2 class="title" style="clear: both"><a id="autocommit"></a>Auto Commit</h2>
          </div>
        </div>
      </div>
      <p>
            While transactions are frequently used to provide atomicity to
            multiple database 
            
            operations, it is sometimes necessary to perform
            a single database 
            
            operation under the control of a transaction.
            Rather than force you to obtain a transaction, perform the single 
            write operation, and then either commit or abort the transaction,
            you can automatically group this sequence of events using
            <span class="emphasis"><em>auto commit</em></span>.
        </p>
      <p>
            To use auto commit:
        </p>
      <div class="orderedlist">
        <ol type="1">
          <li>
            <p>
                        Open your environment and your databases 
                        
                        so that they support
                    transactions.  See <a class="xref" href="enabletxn.html" title="Chapter 2. Enabling Transactions">Enabling Transactions</a> 
                    for details.
                </p>
            <p>
                    Note that frequently auto commit is used for the environment
                    or database open.  To use auto commit for either your
                    environment or database open, specify 
                    <code class="literal">DB_AUTO_COMMIT</code> to the 

                    <code class="methodname">DB_ENV-&gt;set_flags()</code>
                    
                    or
                    <code class="methodname">DB-&gt;open()</code>
                    
                    method. If you specify auto commit for the environment
                    open, then you do not need to also specify auto commit
                    for the database open.
                </p>
          </li>
          <li>
            <p>
                    Do not provide a transactional handle to the method that is
                    performing the database 
                        
                    write operation.
                </p>
          </li>
        </ol>
      </div>
      <p>
            Note that auto commit is not available for cursors. You must always
            open your cursor using a transaction if you want the cursor's
            operations to be transactional protected. See 
            <a class="xref" href="txncursor.html" title="Transactional Cursors">Transactional Cursors</a> for details on using
            transactional cursors.
        </p>
      <div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
        <h3 class="title">Note</h3>
        <p>
                Never have more than one active transaction in your thread
                at a time. This is especially a problem if you mix an
                explicit transaction with another operation that uses auto
                commit. Doing so can result in undetectable deadlocks.
            </p>
      </div>
      <p>
            For example, the following uses auto commit to perform the database write operation:
        </p>
      <pre class="programlisting">#include &lt;stdio.h&gt;
#include &lt;stdlib.h&gt;

#include "db.h"

int
main(void)
{
    int ret, ret_c;
    u_int32_t db_flags, env_flags;
    DB *dbp;
    DB_ENV *envp;
    DBT key, data;
    const char *db_home_dir = "/tmp/myEnvironment";
    const char *file_name = "mydb.db";
    const char *keystr ="thekey";
    const char *datastr = "thedata";
    
    dbp = NULL;
    envp = NULL;

    /* Open the environment */
    ret = db_env_create(&amp;envp, 0);
    if (ret != 0) {
        fprintf(stderr, "Error creating environment handle: %s\n",
            db_strerror(ret));
        return (EXIT_FAILURE);
    }

    env_flags = DB_CREATE |    /* Create the environment if it does 
                                * not already exist. */
                DB_INIT_TXN  | /* Initialize transactions */
                DB_INIT_LOCK | /* Initialize locking. */
                DB_INIT_LOG  | /* Initialize logging */
                DB_INIT_MPOOL; /* Initialize the in-memory cache. */

    ret = envp-&gt;open(envp, db_home_dir, env_flags, 0);
    if (ret != 0) {
        fprintf(stderr, "Error opening environment: %s\n",
            db_strerror(ret));
        goto err;
    }

    /* Initialize the DB handle */
    ret = db_create(&amp;dbp, envp, 0);
    if (ret != 0) {
        envp-&gt;err(envp, ret, "Database creation failed");
        goto err;
    }

    db_flags = DB_CREATE | DB_AUTO_COMMIT;
    /* 
     * Open the database. Note that we are using auto commit for the open, 
     * so the database is able to support transactions.
     */
    ret = dbp-&gt;open(dbp,        /* Pointer to the database */
                    NULL,       /* Txn pointer */
                    file_name,  /* File name */
                    NULL,       /* Logical db name */
                    DB_BTREE,   /* Database type (using btree) */
                    db_flags,   /* Open flags */
                    0);         /* File mode. Using defaults */
    if (ret != 0) {
        envp-&gt;err(envp, ret, "Database '%s' open failed",
            file_name);
        goto err;
    }

    /* Prepare the DBTs */
    memset(&amp;key, 0, sizeof(DBT));
    memset(&amp;data, 0, sizeof(DBT));

    key.data = &amp;keystr;
    key.size = strlen(keystr) + 1;
    data.data = &amp;datastr;
    data.size = strlen(datastr) + 1;


    /*
     * Perform the database write. A txn handle is not provided, but the
     * database support auto commit, so auto commit is used for the write.
     */
    ret = dbp-&gt;put(dbp, NULL, &amp;key, &amp;data, 0);
    if (ret != 0) {
        envp-&gt;err(envp, ret, "Database put failed.");
        goto err;
    }

err:
    /* Close the database */
    if (dbp != NULL) {
        ret_c = dbp-&gt;close(dbp, 0);
        if (ret_c != 0) {
            envp-&gt;err(envp, ret_c, "Database close failed.");
            ret = ret_c
        }
    }


    /* Close the environment */
    if (envp != NULL) {
        ret_c = envp-&gt;close(envp, 0);
        if (ret_c != 0) {
            fprintf(stderr, "environment close failed: %s\n",
                db_strerror(ret_c));
            ret = ret_c;
        }
    }

    return (ret == 0 ? EXIT_SUCCESS : EXIT_FAILURE);
} </pre>
    </div>
    <div class="navfooter">
      <hr />
      <table width="100%" summary="Navigation footer">
        <tr>
          <td width="40%" align="left"><a accesskey="p" href="abortresults.html">Prev</a> </td>
          <td width="20%" align="center">
            <a accesskey="u" href="usingtxns.html">Up</a>
          </td>
          <td width="40%" align="right"> <a accesskey="n" href="nestedtxn.html">Next</a></td>
        </tr>
        <tr>
          <td width="40%" align="left" valign="top">Aborting a Transaction </td>
          <td width="20%" align="center">
            <a accesskey="h" href="index.html">Home</a>
          </td>
          <td width="40%" align="right" valign="top"> Nested Transactions</td>
        </tr>
      </table>
    </div>
  </body>
</html>
